The invention relates to a multiple-circuit pressure-medium braking system for vehicle and trailer combinations.
An example of a multiple-circuit pressure-medium braking system for vehicles which is controlled by multi-circuit safety valve is shown in German Offenlegungsschrift No. 3,149,110. In this system, the foot-brake pedal actuates a signal generator which applies an electrical signal to the valve of the front-wheel brake through a first electrical circuit that is supplied by a first battery. By means of this signal, the pressure medium of the first pressure-medium circuit is regulated by the valve of the front-wheel brake and thereby actuates the brake cylinders of the front-wheel brake.
The signal generator actuated by the foot-brake pedal in this system also applies the electrical signal to the valve for the rear-wheel brake through a second electrical circuit supplied by a second battery, so that the pressure-medium of the second pressure-medium circuit is regulated and the brake cylinders of the rear-wheel brake are actuated.
A signal generated by the signal generator for the parking brake is applied to the valve for the parking brake by means of a third electrical circuit supplied from the first and second electrical circuits. This valve regulates the pressure-medium of the third pressure-medium circuit which actuates the cylinders of the parking brake.
Lastly, the trailer control valve is connected to the two electrical circuits of the service brake and, through a further electrical connection, to the signal generator for the parking brake. The trailer control valve regulates the pressure-medium which is supplied to the third pressure-medium circuit through a supply line branched off from this circuit. By means of the regulated pressure-medium, the brake valve in the trailer is controlled by a coupling head.
A disadvantage of the above system is that the electrical control system has only two circuits, supplied by only two independent batteries, even though three pressure-medium circuits are provided for the safety of the braking system. If a battery fails, it is no longer possible to control at least a part of the braking system.
Another disadvantage is the number of different valves in the system, some of which are controlled by two or even three electromagnets. Valves of this type are of complicated design and are relatively expensive. Moreover, a trailer control valve controlled by three electromagnets is technically difficult to produce, since signals of different polarities are applied to the trailer control valve from the service-brake circuits and from the brake circuit of the parking brake.
A further disadvantage is that the trailer brake reacts only after a long response time, since the brake valve of the trailer brake is controlled by the regulated pressure-medium of the trailer control valve. Also, because of the delayed build-up of the control pressure there exists the danger that the trailer will not be braked when the vehicle is braked. The lack of contact-breaking protection is an additional disadvantage.
Numerous proposals have been made for reducing the time delay between tractor and trailer brake initiations with electrical means.
An object of the present invention is the development of a multiple-circuit pressure-medium braking system for vehicles which is controlled by a multi-circuit safety valve arrangement, that guarantees maximum possible safety by allowing the front-wheel brake, the rear-wheel brake and particularly the trailer brake to respond at the same time.
This and other objects of preferred embodiments of the invention are attained by providing a multiple circuit pressure-medium braking system for vehicle and trailer combinations with a plurality of pressure-medium circuits, a pressure-medium supply means for supplying a pressure-medium, and a plurality of electrical circuits. Each electrical circuit controls the flow of the pressure-medium in a corresponding pressure-medium circuit. Also provided is a trailer brake valve for controlling the supply of pressure-medium to the brake cylinder of the trailer, and a trailer control valve which is fluidically connected to the trailer brake valve and fluidically controls the operation of the trailer brake valve. Further, a means for indirectly controlling the operation of the trailer brake valve is provided.
In advantageous preferred embodiments of the invention, it is provided that each electrical circuit is provided with its own battery in addition to the vehicle battery with this arrangement, in the event that either an additional battery or the vehicle battery fails, the braking system remains fully functional, thus guaranteeing maximum possible safety. Furthermore, the braking system also functions on vehicles delivered without a vehicle battery, with the result that maneuvering becomes possible, this being especially advantageous when transport vehicles are loaded and unloaded by means of such maneuvering.
A further substantial advantage of preferred embodiments of the invention is that the brake valve in the trailer, in addition to being controlled fluidically, is also controlled electrically, thereby making it possible for the trailer to be braked at the same time as the motor vehicle. In particular, this prevents the trailer from colliding into the back of the motor vehicle.
Further features of preferred embodiments of the present invention provide further additional advantages. For example, by means of an electrical variable resistor, a signal inversely proportional to the pressure of the vehicle parking brake is formed, as a result of which the trailer control valve can be controlled by signals of the same polarity both from the service brake and from the parking brake.
According to advantageous features of preferred embodiments, a one-way valve prevents automatic actuation of the vehicle parking brake if a defect in a pressure-medium circuit occurs during driving.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings, which show for purposes of illustration only, an embodiment constructed in accordance with the present invention.